If several clients are allowed to perform control operations
simultaneously, this method should not be used by more than one of
the multiple clients in question.
Exception codes
Only a few exception code alternatives exist for control structures:
• 01 = illegal function
• 02 = illegal address
• 03 = illegal value
The exception code 03 is also returned if a command operation is rejected due to other
internal reasons. An additional internal reason code for the exception, can be found in
the SSR6 register after the command operation.
The primary internal rejection reasons for control structure write operations may be
for example:
• The Modbus control structure write has timed out (15 sec).
• The client has no write authority.
• The IED is in the local or OFF state.
• The control operation is blocked, that means already reserved, by another client.
If a positive acknowledgement is returned, the control command has been initiated
inside the IED.
3.4.6.3 Additional control operation features
Normal or enhanced security operations
Control objects on IED system level (IEC 61850 level) always follow a control model.
Control model alternatives are referred to as normal-security or enhanced-security.
Some control objects has a fixed control model. Other objects' control models are
configurable. On Modbus level this means:
Normal security object
• Positive confirmation means that the control has been activated and the
application behind the control point has performed successfully.
• Exception 03 response from a normal-security object means that either the
control is not activated, or the control is activated, but the application behind the
control point does not perform successfully.
1MRS757645 B Section 3
Vendor-specific implementation
620 series 35
Communication Protocol Manual
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